KNIFEFISH ID

Gymnotus Catanaipo, maybe? I'm not a Knife expert though.
Nice Knife though. I would have grabbed it for $15.

It's impossible for it to be a hybrid, but there are many many species in the genus gymotus etc that look like this. they are wild caught so they probably didn't know either and just gave it a common name. You can be assured it will grow to at least 2 feet but possibly more like 4-5 for some other species, it is very agressive, and it's life cycle is based on the flooding of the forest, so you may want to keep that in mind to keep it happy (let the water evaporate a lot and get nasty then add a lot of rodi at once AT LEAST - you can get even more into this but do that at least once a year otherwise it may stress) they build nests out of sticks and when they do that they'll bite your hand off if you try to mess with the tank.